The invention is based on a measuring instrument for contactless ascertainment of a rotation angle according to the preamble to claim 1. The prior art, for example DE 197 53 775.8 A1, has disclosed using flux conducting parts made of magnetically conductive material in these measuring instruments in order to guide the magnetic lines. But these measuring instruments are consequently relatively large and can only be partially incorporated into measuring systems. Furthermore, in this embodiment, the slope of the linear region of the measurement curve cannot be influenced to a sufficient degree.
In the sensor according to DE 197 12 833 A1, a permanent magnet is disposed on a magnet wheel which moves past a magnetoresistive sensor. In this instance, only short peaks in the measurement curve are produced, which are used as triggering or counting pulses.
DE 196 29 611 A1 describes a measuring instrument which has a number of stationary Hall elements. A rotor made of soft magnetic material is moved past these Hall elements so that the distance between each Hall element and the rotor continuously changes. Each Hall element has a permanent magnet rigidly attached to it, which generates the magnetic flux. For the determination of the measurement value, the rotor must consequently also be a flux conducting part.
In the rotation angle detector according to DE 40 14 885 A1, the permanent magnet has flux conducting parts so that between the poles of the magnet, a magnetic field is produced with magnetic flux lines that are as parallel as possible and a flux density that is as uniform as possible.
In the rotation angle sensor described in DE 196 35 159 A1, magnets are moved past one or more reed contacts, wherein the rotation angle can only be measured in steps.
The measuring instrument according to the invention, for contactless ascertainment of a rotation angle, with the characterizing features of claim 1, has the advantage over the prior art that by means of virtually arbitrary positioning of the magnetic field sensitive element which produces the output signal, a slope of the linear region of the measurement curve can be influenced. The linear region thus produced can be greater than 80xc2x0. A relatively small magnet can be used which is simply clipped or glued to the support plate of the rotor or can also be injection molded in a plastic. Assembly costs can be sharply reduced by eliminating the flux parts that are otherwise customary in contactless sensors. Large geometric tolerances in the magnet are permissible due to the design of the sensor itself. Since the magnet has a homogeneous magnetic field in the vicinity of the center of the Hall element, it is not susceptible to axial displacement and the accompanying tolerance fluctuations. The characteristic curve itself is composed of a steep region and a flat region so that large angles can be associated with the flat region and small angles can be associated with the steep region.
Advantageous modifications and improvements of the measuring instrument disclosed to claim 1 are possible by means of the steps taken in the dependent claims.